Conventionally, a device applied for an electrophotographic system, e.g. an image forming member such as a photocopier, printer, and facsimile, generally contains a rotatable photoconductor drum, and forms a latent electrostatic image on the photoconductor drum by uniformly charging a photosensitive layer of the photoconductor drum, followed by exposing the charged photosensitive layer of the photoconductor drum with laser beams emitted from a laser scanning unit. The image forming apparatus further contains a system for operating the following process. Namely, after developing the formed latent electrostatic image with a toner, the developed image is transferred to a transfer paper as a recording material, and is then thermally fixed on the transfer paper by passing the transfer paper through a thermal fixing device.
The fixing member having sufficient elasticity for attaining the fixing ability suitable for color images, however, has a problem that it has poor abrasion resistance, and release properties for a toner.
The fixing system generally applies a fixing system for fixing a toner image on a recording sheet by passing the recording sheet between a fixing roller or fixing belt and a pressure roller in contact with the fixing roller or belt with a certain pressure, and softening and pressurizing the deposited toner on the recording sheet with sheet.
Since the fused toner image is brought into contact with a fixing member in this fixing system, a surface layer of the fixing member is formed in the film thickness of 15 μm to 30 μm with a material having high release properties (e.g. a fluororesin). This material, however, has a disadvantage that the material has a high degree of hardness due to the characteristics of the resin. If the material has the high degree of the hardness, the material cannot correspond to the irregularities of the paper fibers when the toner image electrostatically formed is fixed by heat and pressure, and therefore high quality images cannot be formed. Especially, because of the polularities of full-color image formation, the fixing is currently performed on a plurality of color toners in the manner that the fixing member is brought into contact with the color toners to cover the shapes of the toners to thereby melt the color toner. Therefore, the hardness of the material greatly affects the fixation and resulting images.
To solve this problem, a method for forming an elastic material (e.g., silicone rubber and fluororubber) on a surface of a fixing member has been applied.
By using the elastic material to the fixing member, the correspondence to the irregularities of the paper fibers can be improved. This fixing member however cannot secure the degree of the durability to the same level as that of the fluororesin. Therefore, the fixing member using the elastic material tends to be scratched by the frictions with transfer paper or by the scratches formed on the transfer paper by a separation claw for separating the transfer paper. These scratches are transferred during the fixing process to thereby form abnormal images. Moreover, as a conventional technique, it is known that a large amount of silica powder or alumina powder is formulated into a silicone rubber composition of an elastic material for the purpose of improving abrasion resistance. This silicone rubber however has high rubber hardness, which as described earlier, cannot attain sufficient elasticity to provide high quality images. Therefore, there is proposed an invention which related to a material for improving the hardness of the elastic material by reducing crosslink density to provide low hardness of the rubber, for example as in PTL 1. In this case, however, inorganic fillers may fall out as the rubber strength reduces, and therefore sufficient abrasion resistance cannot be attained. Depending on the conditions, the inorganic filler functions as an abrasion agent, which may accelerate abrasion in some cases.
Further, a fixing member using an elastic material cannot secure its release properties to the extend that that of the fluororesin does, and therefore offset needs to be prevented by coating or dipping the fixing member with or in a compatible low molecular oil component to supplement the release properties. In this method, however, there are various problems such as staining transfer paper by smearing of the oil component during the standing period, a problem in maintenance, and problem in continuity of the release ability, and furthermore there is a problem that a device is required for supplying a liquid for preventing offset, which makes a configuration of a fixing device complex. Accordingly, based on the insight that a liquid for preventing offset is supplied from inside toner particles during heating without using silicone oil, there is proposed a method for adding a releasing agent to a toner (see, for example, PTL 2 to PTL 4). When a large amount of the additive is added to obtain a sufficient release effect, filming on a photoconductor, or surface deposition on a toner bearing member (e.g. a carrier or sleeve) occurs, which degrades resulting images and such resulting images have problem on practical use. Therefore, it is important to add a releasing agent to a toner in a small amount but sufficient enough to prevent deterioration of images. From this point of view, there is a demand for a fixing member having higher release properties.
PTL 5 discloses a fixing member which uses an so organic inorganic hybrid material obtained by heating a sol containing a metal alkoxide and a solid silica compound to form a gel, as an elasticity material, to thereby improve heat resistance and release properties, but it has not yet been brought into practice.